This invention relates generally to heat pump systems and, more particularly, to a method and apparatus for enhancing the process of defrosting the outdoor coil thereof.
In conventional heat pump system operation, when the system is operating in the heating mode with the outdoor coil acting as an evaporator, the formation of frost or ice on the heat exchanger is a common phenomenon. That is, under appropriate ambient conditions, the media in flowing heat transfer relationship with the evaporator, typically air, has its temperature lowered below its due point, thus causing condensation to form on the coil. If the ambient temperature conditions are sufficiently low, this condensation will then be caused to freeze. That is, since the heat pump operating in the heating mode requires the refrigerant to be at a lower temperature than the ambient air in order to transfer heat thereto by way of the outdoor coil, condensation, and eventually ice or frost, will tend to form on the coils even at ambient temperatures above the freezing point. Once this ice or frost coats the surface of the heat exchanger, the efficiency thereof is impaired, and overall system efficiency is decreased. Consequently it is desirable to maintain the evaporator surfaces free from ice or frost. A defrost cycle is therefore periodically used as a normal mode of operation for that purpose.
A conventional manner of defrosting the outdoor coil is that of reversing the refrigerant flow, such that the outdoor coil functions as a condenser with the hot gases that are discharged from the compressor being circulated directly to the outdoor coil to melt the ice that is formed thereon. During this process, the outdoor fan is normally shut off so that the exposure of the outdoor coils to the cooler ambient temperature of the air does not adversely effect the defrost cycle. While this does speed up the defrost process by inhibiting the flow of ambient air over the coil, it also allows the heat from both the coil and the compressor to flow upwardly by natural convection to be lost to the atmosphere.
It is therefore an object of the present invention to provide a heat pump with an improved defrost cycle.
Another object of the present invention is the provision in a heat pump system for inhibiting the loss of heat by convection during the defrost cycle.
Yet an other object of the present invention is the provision in a heat pump for reducing the time required for a defrost cycle.
Still another object of the present invention is the provision for a heat pump system which is economical to manufacture and economical and effective in use.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.